Insect Control by Physical Means

Some of the important measures for the control of injurious insects have been discussed in the preceding chapter. For the most part these may be classed as indirect methods, since they are intended largely to prevent attack or injury, and are a part of general farm practices adopted for various reasons besides those relating to insects.

On the other hand there are measures that are intended directly to accomplish the destruction of a given pest or to prevent its attack, and are adopted primarily for that purpose.

First among these are a number of simple methods that naturally suggest themselves in the case of the larger insects or those that congregate in limited areas; such as hand picking or burning. Measures of this kind require no special apparatus, and often are effective. They may or may not presuppose accurate knowledge of the life history or habits of the insect dealt with; but often such knowledge is essential if any real benefits are to be secured.

Hand Picking

Hand picking, jarring, or brushing is a common practice in dealing with such insects as the tomato worm, squash bugs, and the like. It is worth knowing that a mass of such insects collected in a box or other receptacle can easily be killed.

Burning

Burning is often a prompt and effective remedy, especially with caterpillars that tend to congregate in masses. A familiar example is seen in the common tent caterpillar.

A torch is conveniently made by tying a ball of rags tightly on the end of a pole, and soaking with kerosene, taking care not to use so much of the liquid that it runs down the pole.

Destroying Egg Masses

In the control of some caterpillars, banding the trees is simple and effective; but it is absolutely worthless against others. Its value depends on the characteristics of the insect to be dealt with. Thus, in the case of the cankerworm infesting apple trees, the adult female happens to be wingless, and must crawl up the trunk to lay her eggs. A sticky band will stop her from going up to the branches, and if the band is maintained until the young worms have hatched and they in turn are thus prevented from ascending the tree, no damage can be done to the foliage. But this band would be useless as a means of preventing a winged moth, such as the parent of the tent caterpillar, from gaining access to the tree. Bands are of value also where it is desired to prevent cater pillars that have hatched on adjacent land from migrating to trees that had been protected or cared for.

Covering with Cloth or Screen

Usually this plan is made use of a prevent injury to young plants, until they have grown large enough to withstand attack. Young melon or squash plants are therefore protected from injury by the striped cucumber beetle.

Where cloth is used, it should be of thin texture. Common cheesecloth serves the purpose very well. Handy covers are made by cutting a barrel hoop into two pieces, crossing these at a right angle, tacking the ends to a second hoop, and covering this frame with cloth. Such frames may be packed away for storage, one within another, taking up little room.

Wire screening may be shaped into cones, which are used in the same way as the cloth covered frames, and have a similar advantage of packing away in small space. If galvanized wire is used and properly stored when not needed, it will no rust for several years; but the first cost is rather heavy as compared with cheesecloth frames.

Destroying Borers

Cutting out borers with a knife is a remedy that seems drastic, but it may be the only means of putting a stop to an injury that would otherwise prove fatal.

Frequently, it is possible to kill the borer by probing the burrow with a soft copper wire. If the end of the wire is nicked, so as to give it a few rough barbs, it will bring the borer or a piece of him out with it, and the operator may thus know whether he has succeeded in reaching the culprit.

If cutting is necessary, a sharp knife should be used and the course of the burrow carefully followed. In this way no more real damage will be done to the tree than has already been done by the borer itself. It is well to paint the wound afterward with a mixture of lead and linseed oil, not with ready mixed paint, which is apt to contain injurious oils added as driers.

Removal of Dead or Dying Limbs

There are certain species of small borers that attack especially trees that have been weakened. Once started, they continue to breed in such places, rapidly killing the tree and spreading from it to others in the neighborhood that do not happen to be growing as vigorously as might be. By prompt removal of the infested limbs or trees the pests may be eliminated and other trees near by saved from attack. This, in fact, is the only feasible means of control in the case of some insects, such as the shot hole borer. The limbs or trees removed should be converted at once into cordwood and burned. Otherwise, little will be gained by their removal.

Use of Traps

The kinds of traps are legion, and range all the way from chips or stones placed in the garden for squash bugs to hide under to more or less ingenious devices for capturing roaches and flies. Many are efficient, thought it often seems that new individuals make their appearance about as fast as the others are caught. At best the total numbers merely are reduced.

A variation of traps is seen in the use of trap crops. By this device some kind of plant is introduced that the pest is fond of, and after the insects have collected on these plants, they are destroyed by poisoning, burning, or by spraying them with some chemical. In other cases the trap precedes the regular crop, and thus diverts attack from the more valuable plant. Thus, early kale is sown in fields that later are to be set out to cabbages, in order to attract the over wintering adults of the harlequin cabbage bug.